MICROMORPHOLOGICAL INDEX FOR THE EVALUATION OF SOIL EVOLUTION IN CENTRAL SPAIN

Micromorphological indices for the evaluation of the degree of soil evolution are established on the basis of micromorphological properties. The indices are applied to a chronosequence of soils formed on fluvial terraces. The indices, which reflect microstructural properties, characteristics of fine material and groundmass birefringence, illuvial clay pedofeatures and the prevalence of illuvial clays, all increased steadily with soil age. Soil/age dispersion plots fit linear, power and logarithmic regression equations, with high correlation coefficients and levels of significance. Carbonate indices showed similar trends, although with much greater dispersions. Indices for organic matter, hydromorphy and mineralogical alterations showed clear tendencies to increase in younger soils. The change in the index values with soil age did not support the appearance of a steady state at any time.